Q. This is a broad complex tachycardia. What are your differentials?A. Ventricular tachycardia, SVT with aberrancy (including concealed accessory pathways)

Q. Can you identify the 8 features that help you to differentiate this ECG?A. Answers labelled on following ECG

Very broad QRS >160ms

Concordance across chest leads – however, though all positive, V4 and V5 have RS waves

Positive aVR, however not quite the extreme NW axis deviation

Capture beat – narrow QRS complex (circled in lead III)

Fusion beat – a hybrid between a sinus beat and a VT beat (circled in lead V2)

AV dissociation (labelled in the rhythm strip)

RBBB V1 morphology: Taller left ‘rabbit ear’ compared to right ear, the opposite to typical RBBB

Brugada’s sign – The distance from the onset of the QRS complex to the nadir of the S-wave is > 100ms in one praecordial lead (best seen in V6)

What about if you were to look at this ECG using the Brugada criteria? Brugada et al, Circulation 1991;83:1649Well it helps you, but is not definitive. If the answer to these questions is yes then it is more sensitive for VT, if the answers are no then it points to SVT with aberrancy.

Absence of RS complex in all leads V1-6

Is the interval from beginning of R wave to nadir of S wave >0.1s in any RS lead?

Are AV dissociation, fusions, or captures seen?

Are there morphology criteria for VT present both in leads V1 and V6?

So it’s not easy. However, don’t rely just on the ECG. Treat the patient in front of you. No diagnostic pathway or criteria are absolute. And if there’s any doubt, treat as VT. So now for some clinical information... This ECG was taken from an 82 year old gentleman with a history of ischaemic cardiomyopathy, metallic mitral valve replacement and CRTD in situ. Clearly the VT in this case was below the device ATP rate.